Perhaps you're correct but my math says that if you quit after winning the first bet or if you lose your first bet and you quit after the second bet then mathematically your expected value is:
EV = 0.5 X $3000 + 0.25 X -$3000 + 0.25 X $0 = $750
So you're expected value is a profit of $750 although the actual "profit" you'll have at the end is either $3000, -$3000, or $0.